The present invention relates to a planetary gear unit for use in an automatic transmission.
Generally, planetary gear units of a double pinion type (called Ravigneaux type) are used in automotive automatic transmissions. Such a planetary gear unit, as described in Japanese Patent Application Laid-Open Publication No. HEI 10-169728 (paragraph 0023, FIG. 4), includes first and second sun gears that are each rotatably supported on an input shaft, a plurality of short pinions that mesh with the first sun gear and are disposed on a circumference thereof, a plurality of long pinions that mesh with the short pinions and the second sun gear and that are disposed on a circumference thereof, a ring gear that meshes with the long pinions, and a carrier that rotatably supports each of the short pinions and the long pinions.
As shown in FIG. 7, a related-art carrier 100 used in a double pinion-type planetary gear unit includes two members: a cylinder-shaped first carrier body 106 provided with a flange portion 105 that supports an end of each of support shafts 103, 104 that rotatably support the short pinions 101 and the long pinions 102, respectively; and a second carrier body 108 provided with a flange portion 107 that is spaced from the flange portion 105 of the first carrier body 106 by a predetermined distance in an axial direction, and that supports another end of each of the support shafts 103, 104. The flange portion 107 of the second carrier body 108 is engaged with a bridge connecting portion 110 formed in the flange portion 105 of the first carrier body 106, by a plurality of circumferential bridge portions 109 that extend in the axial direction, and is joined together therewith by a weld W0.